Bug 1559285 - Add webgl.default-antialias. r=mccr8,lsalzman

Default to false on Android, matching existing behavior.

Differential Revision: https://phabricator.services.mozilla.com/D34985

--HG--
extra : moz-landing-system : lando

dom/canvas/WebGLContext.cpp

@@ -98,7 +98,8 @@ using namespace mozilla::layers;
 
 WebGLContextOptions::WebGLContextOptions() {
   // Set default alpha state based on preference.
-  if (StaticPrefs::WebGLDefaultNoAlpha()) alpha = false;
+  alpha = !StaticPrefs::WebGLDefaultNoAlpha();
+  antialias = StaticPrefs::WebGLDefaultAntialias();
 }
 
 bool WebGLContextOptions::operator==(const WebGLContextOptions& r) const {
@@ -349,7 +350,6 @@ WebGLContext::SetContextOptions(JSContext* cx, JS::Handle<JS::Value> options,
   newOpts.stencil = attributes.mStencil;
   newOpts.depth = attributes.mDepth;
   newOpts.premultipliedAlpha = attributes.mPremultipliedAlpha;
-  newOpts.antialias = attributes.mAntialias;
   newOpts.preserveDrawingBuffer = attributes.mPreserveDrawingBuffer;
   newOpts.failIfMajorPerformanceCaveat =
       attributes.mFailIfMajorPerformanceCaveat;
@@ -358,13 +358,16 @@ WebGLContext::SetContextOptions(JSContext* cx, JS::Handle<JS::Value> options,
   if (attributes.mAlpha.WasPassed()) {
     newOpts.alpha = attributes.mAlpha.Value();
   }
+  if (attributes.mAntialias.WasPassed()) {
+    newOpts.antialias = attributes.mAntialias.Value();
+  }
 
   // Don't do antialiasing if we've disabled MSAA.
-  if (!StaticPrefs::MSAALevel()) {
+  if (!mMsaaSamples) {
     newOpts.antialias = false;
   }
 
-  if (!StaticPrefs::WebGLForceMSAA()) {
+  if (newOpts.antialias && !StaticPrefs::WebGLForceMSAA()) {
     const nsCOMPtr<nsIGfxInfo> gfxInfo = services::GetGfxInfo();
 
     nsCString blocklistId;
@@ -1272,7 +1275,7 @@ void WebGLContext::GetContextAttributes(
   result.mAlpha.Construct(mOptions.alpha);
   result.mDepth = mOptions.depth;
   result.mStencil = mOptions.stencil;
-  result.mAntialias = mOptions.antialias;
+  result.mAntialias.Construct(mOptions.antialias);
   result.mPremultipliedAlpha = mOptions.premultipliedAlpha;
   result.mPreserveDrawingBuffer = mOptions.preserveDrawingBuffer;
   result.mFailIfMajorPerformanceCaveat = mOptions.failIfMajorPerformanceCaveat;

dom/webidl/WebGLRenderingContext.webidl

@@ -37,13 +37,15 @@ typedef unsigned long long GLuint64EXT;
 enum WebGLPowerPreference { "default", "low-power", "high-performance" };
 
 dictionary WebGLContextAttributes {
-    // boolean alpha = true;
-    // We deviate from the spec here.
-    // If alpha isn't specified, we rely on a pref ("webgl.default-no-alpha")
-    GLboolean alpha;
+    // We deviate from the spec for alpha and antialias:
+    // * alpha: Historically, we might use rgb565 instead of rgb(x)8, for 
+    //          memory bandwidth optimization.
+    // * antialias: On Android, DPI is high and mem-bandwidth is low, so we 
+    //              default to antialias:false if it's not set.
+    GLboolean alpha; // = true; // Default is controlled by webgl.default-no-alpha.
     GLboolean depth = true;
     GLboolean stencil = false;
-    GLboolean antialias = true;
+    GLboolean antialias; // = true; // Default is controlled by webgl.default-antialias.
     GLboolean premultipliedAlpha = true;
     GLboolean preserveDrawingBuffer = false;
     GLboolean failIfMajorPerformanceCaveat = false;

modules/libpref/init/StaticPrefList.h

@@ -7228,6 +7228,19 @@ VARCACHE_PREF(
   RelaxedAtomicBool, true
 )
 
+#ifdef MOZ_WIDGET_ANDROID
+# define PREF_VALUE false
+#else
+# define PREF_VALUE true
+#endif
+VARCACHE_PREF(
+  Live,
+  "webgl.default-antialias",
+  WebGLDefaultAntialias,
+  RelaxedAtomicBool, PREF_VALUE
+)
+#undef PREF_VALUE
+
 VARCACHE_PREF(
   Live,
   "webgl.default-low-power",

modules/libpref/init/all.js

@@ -4632,12 +4632,6 @@ pref("image.webp.enabled", true);
 pref("canvas.image.cache.limit", 0);
 
 // WebGL prefs
-#ifdef ANDROID
-// Disable MSAA on mobile.
-pref("gl.msaa-level", 0);
-#else
-pref("gl.msaa-level", 2);
-#endif
 pref("gl.require-hardware", false);
 #ifdef XP_MACOSX
 pref("gl.multithreaded", true);